Intermittent pneumatic compression is the technique of cyclically compressing a limb with air pressure so as to enhance the circulation of blood. In such prior art systems, pressure is applied from a source of compressed air by a control mechanism to provide a pulse of pressure that intermittently inflates a cuff enveloping all or part of an arm or leg. The rapid inflation of the cuff serves to rapidly force blood out of the veins. The pressure in the cuff is then released, allowing the veins to refill. Parameters that can be controlled include the rate of pressurization, the pressure achieved, the time period of the compression, the rate of depressurization, the time period between pulses, and the total duration of the application of intermittent pneumatic compression. As disclosed in U.S. Pat. No. 5,496,262, assigned to the common assignee and incorporated herein by reference, IPC can also be applied by means of cuffs having more than one chamber, the chambers being disposed at relatively distal and proximal locations along the limb. Additional parameters that can be controlled with multiple-chambered cuffs include the level of pressure that can be provided to each chamber (i.e., graduated compression), and the timing of the application of pressure to each chamber (i.e., sequential compression).
IPC as practiced in the prior art provides enhanced circulation of blood, which is known to be of therapeutic benefit for a variety of circulatory disorders. For example, the use of IPC is known in the prevention and treatment of edema. IPC is also known as a means for reducing the risk of deep vein thrombosis (DVT). U.S. Pat. No. 5,588,955, also assigned to the common assignee and incorporated herein by reference, discloses a method and apparatus for applying graduated and/or sequential IPC to a limb to prevent DVT. Applicant's assignee also manufactures and sells devices under the trademarks VENAFLOW® and ARTERIALFLOW® which are used to apply IPC to a patient in need of such therapy.
As disclosed in the aforementioned U.S. Pat. Nos. 5,496,262 and 5,588,955, in IPC as used in the prior art the period of compression is typically short, about ten seconds, and the recovery period between pulses is about a minute, to allow the veins to refill after being rapidly emptied by the short pulse of compression. The optimal amount of compression used in prior art devices is in the range of 35–45 mmHg. Further, it is known that the velocity of venous flow during the period of compression is proportional to the rate of pressurization. For example, a pulse that reaches maximum pressure in six seconds will have a much greater effect on venous velocity than a pulse that reaches the same maximum pressure in 30 seconds.
It has been suggested in the medical literature that application of prolonged compression may promote healing of a bone fracture. In “Acceleration of Fracture Healing Distal to a Venous Tourniquet,” R. L. Kruse, et al., J. Bone and Joint Surgery, vol. 56-A, No. 4, June 1974, it was reported that the continuous use of a hand-wrapped venous tourniquet was shown to increase new bone formation at fracture sites and in defects in bone, and to accelerate fracture healing. In “A New Concept in Fracture Immobilization: The Application of a Pressurized Brace,” P. A. Dale, et al., Clinical Orthopaedics and Related Research, No. 295, pp. 264–269, 1993, it was found that continuous use of a static pressurized brace made by Aircast, Inc. of Summit, N.J., the assignee of the instant application, yielded a stronger healed fracture than did a traditional cast. The pressurized brace in that study provided an average skin-to-brace pressure of about 29 mmHg; applied constantly for at least six weeks.
In “Venous Pressure and Bone Formation,” Kelly, et al., Microvascular Research, 39, 364–375 (1990), a specially designed venous tourniquet from Aircast was applied continuously for several weeks to broken bones in animal limbs. Those limbs in which venous pressure was increased with the continuous application of the venous tourniquet compression experienced an increase in new bone formation.
In “Investigation of the Role of Venous Pressure in Bone Changes During Prolonged Weightlessness,” McCarthy, Journal of Gravitational Physiology, Vol. 3 (2), (1996), a venous tourniquet system (VTS) comprising an intermittent pneumatic compression system in which a peak pressure of 60 mmHg is applied in a cycle of 30 seconds on/30 seconds off for a total time of one hour per day in conditions of weightlessness was studied to determine if the VTS would prevent bone loss normally associated with prolonged weightlessness. Conclusive data from this study has not yet been published.
Prior attempts at using continuously applied venous tourniquet compression for the promotion of fracture healing have not been fully successful because of the pain and discomfort to the skin of the patient resulting from the continuous application of the tourniquet. Continuously applied tourniquet compression could also create other undesirable side effects such as transient neuropathy, edema, and soft tissue damage related to ischemia.
Thus one object of the invention to provide a method for facilitating the healing of bone fractures yet which minimizes undesirable side effects including skin discomfort and related disorders that can arise from continuously applied tourniquet compression.
It is another object of the invention to provide an apparatus for facilitating the healing of bone fractures yet which minimizes undesirable side effects including skin discomfort and related disorders that can arise from continuously applied tourniquet compression.